1. Field of the Invention
The invention is directed to a method of preparing inorganic phosphate aerogels and, in particular, inorganic phosphate aerogels in the form of granular material characterized by high surface area and pore volume.
2. Relevant Art
Inorganic oxide aerogels, specifically metal oxide aerogels, are well known in the art as suitable for a variety of applications such as catalysts, catalyst supports, absorbents, chromatographic column packing, anti-caking agents, viscosity enhancers, pigments, opacifiers, as well as ceramics, smoke suppressants, abrasives, dentifrice polishing agents and the like. The product of the instant application can be similarly utilized and can additionally be used as a surfactant.
The preparation of aerogels, in general, and silica aerogels, in particular, has been well documented in the art. U.S. Pat. Nos. 2,249,767; 2,672,833; 2,093,454 and 4,327,065 all disclose processes for producing aerogels. In addition, an article entitled Inorganic Oxide Aerogels appearing in Advances in Colloid and Interface Chemistry, Vol. 5, pages 245-273 (1976) published by Elsevier Scientific Publishing Co., Amsterdam, also describes methods of producing various aerogels.
It has been known to produce such aerogels by hydrolyzing salts, or alkoxides, in the presence or absence of a catalyst, generally an acid or base, to form a gel which is washed with water and then solvent exchanged with an alcohol prior to conventionally drying in an autoclave at the critical temperature and pressure of the solvent.
Co-pending application Ser. No. 565,937 discloses a process of preparing inorganic oxide aerogels wherein the solvent is extracted from the aged aerogel in an autoclave using an extraction fluid.
U.S Pat. Nos. 3,271,299 and 3,342,750 describe the preparation and use of an alumina-aluminum phosphate gel which is prepared by reacting aluminum chloride with phosphoric acid and ethylene oxide. This prior art technique produces a granular product which is sensitive to water and difficult to form into a catalyst shape since it loses a substantial part of its surface area during the forming process.
U.S. Pat. Nos. 3,271,299 and 3,342,750 describe the preparation and use of an alumina-aluminum phosphate cogel which is prepared by reacting aluminum chloride with phosphoric acid and ethylene oxide.